As the number of battery powered and mobile devices used by consumers has grown, people are interested in wireless power transfer systems that can be used to recharge or directly power those mobile devices. Recently, wireless power transfer systems have become commercially available that utilize near-field or inductive power transfer techniques and that require the power transmitter and receiver be very close to each other, if not actually in physical contact. Resonant inductive systems using high-Q resonator structures promise to transfer power more efficiently and over longer distances than inductive systems, but have yet to be widely deployed in the market place. Both traditional and resonant induction are sometimes referred to as non-radiative and/or near-field power transfer techniques, because the distance over which power is transferred is in the near-field of the inductive coils themselves. Therefore, the distance over which power may be efficiently transferred using non-radiative techniques is typically limited to one meter or less.
Near field or non-radiative wireless power transfer techniques are often contrasted to radiative techniques which in general are less efficient and which transfer power using propagating or radiated electromagnetic fields. While directed radiated electromagnetic radio waves can be used to transfer power efficiently over long distances, such systems have not been used in consumer applications because of performance concerns in non-line-of-sight environments and safety concerns of living beings' interaction with the directed energy beams as they propagate from the transmitter to the receiver. Omni-directional radiative schemes, sometimes referred to as direct transmission (DT) schemes, and similar if not the same as information transmission schemes, have relatively lower power transfer efficiency as much of the power radiated by a wireless transmitter is lost in free space. Power harvesters of ambient radio waves have been found some applications in very low power applications such as powering sensors, but are generally hampered by their inability to capture significant amounts of power or to capture less significant amounts of power in reasonable time frames.
Therefore, there is a need to provide a far-field/radiative wireless power transfer system to address the above-mentioned issues.